The present technology described herein relates to techniques for obtaining positional information about one or more objects. More specifically, the technology described herein relates to methods of and apparatus for determining distance and angular positional information of an object or a plurality of objects with respect to a datum.
Many possible applications of exemplary embodiments are envisaged. One specific field of application is within the automotive industry where an exemplary system might be deployed on a vehicle with a field of detection within or without the vehicle or both. In general, a reference to a vehicle in this specification may have particular application to a land vehicle, or, more particularly, a motor land vehicle such as a powered road vehicle. The vehicle would usually be wheeled or tracked and/or be incapable of flight.
For example, there exists a known problem with safety air bags that they can cause serious injuries if deployed while a person is sitting too close to the bag. Moreover, if the vehicle were not fully occupied, it would be desirable to deploy only those bags needed to protect the occupants. This would minimise the pressure pulse that is generated within the vehicle upon deployment and also reduce the considerable cost of replacement of the air bags if the vehicle is subsequently repaired. An exemplary embodiment of the present system might be employed to determine the number and position of the occupants in a vehicle and control the deployment of air bags accordingly; such a system could apply to any or all of the air bags, whether side or front air bags. This information could further be used to send an automatic notification to the emergency services in the event of an accident. Use of the system within a vehicle might be extended to act as an intruder detection system, to monitor the contents of a load bay or boot, or even to detect movements of the driver characteristic of an onset of drowsiness.
An exemplary embodiment of the present system could also be employed to determine the relationship between a vehicle and surrounding objects. For example, a system could provide a driver with a manoeuvring aid to avoid contact with objects or people during reversing or parking manoeuvres, and to measure a space to determine whether the vehicle can fit into it. An indication might be provided to warn a driver of the presence of a vehicle in a mirror blind spot to assist the driver when changing lane or merging into traffic. Furthermore, a warning could be issued or the brakes applied to prevent the vehicle from hitting the one in front in slow-moving or congested traffic. Of course, such applications are not limited to use on passenger vehicles. They might equally be applied to commercial vehicles or earth-moving equipment. Such a system can provide an operator of a vehicle with a complete assessment of the situation existing in the vicinity of the vehicle.
An exemplary embodiment of the present system might also have aeronautical applications, such as collision warning for aircraft, or as a landing aid, particularly for helicopters.
Further applications of an exemplary embodiment of the present system might include position monitoring for articles in a handling system such as a production line or articles in a post handling system; intruder detection in a building or an open space as part of a security system; liquid level detection; imaging the interior of a room from outside its walls and gathering information through walls generally; detecting the presence of articles within structures such as walls; amongst many other possibilities.
As a further example, there is often a need to determine the location of objects, such as cables, pipes or reinforcement rods within walls. It is often essential to locate such objects with accuracy prior to carrying out operations on the wall, such as drilling or demolition. An exemplary embodiment of the present system can be used to provide an accurate indication of the location of such objects.
An exemplary embodiment of the present system may also provide data for further processing for classifying, tracking and measuring moving objects.
U.S. Pat. No. 5,829,782 discloses a system for monitoring occupancy of a vehicle. The disclosed system operates by emitting signals within the vehicle and, by means of suitable detectors, monitoring reflections of these waves. The reflected signals are analysed algorithmically using a variety of pattern-recognition techniques to look for the presence of characteristic qualitative and/or quantitative features. The results of the analysis are compared with results obtained under controlled conditions in order to draw an inference about the occupancy of the vehicle. Since the system operates by comparing a signal with previously obtained patterns, it does not enable accurate location of arbitrary objects within its detection field.
WO98/00729, the named “Applicant” of which is the present assignee, discloses a radar system, particularly for use on a vehicle, to provide a driver with a warning of potential obstructions in the vicinity of the vehicle. The system establishes a plurality of static, scanning and tracking range gates at which objects can be detected. The disclosure of WO98/00729 is hereby incorporated into this specification by reference.
WO97/14058, the named “Applicant” of which is the present assignee, discloses a system in which a signal is transmitted into a detection region, and signals reflected from an object in that region are detected at a plurality of locations. By monitoring these reflections as the object passes through a plurality of range gates, the trajectory of the object can be established. While this system is highly effective for its intended purpose, it has been found that it is not ideally suited to detection of objects that are stationary within the detection region. This can limit the effectiveness of such apparatus in applications of the type described above. The disclosure of WO97/14058 is hereby incorporated into this specification by reference.
Angular Resolution by Cross-Correlation
From a first aspect, an exemplary embodiment provides apparatus for obtaining positional information relating to an object, the apparatus comprising:                an (optionally fixed) array comprising a transmitting element and a plurality of receiving elements;        a signal generating stage for applying a series of pulses to the transmitting element to cause it to transmit a signal, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements;        a detection stage for detecting signals reflected to the receiving elements and for generating output signals representative of the received signals; and        a processing stage operable by application of a truncated cross-correlation function to detect, measure or determine the interval between signals received by a plurality of the receiving elements, whereby to determine an angular position of an object from which the transmitted signal has been reflected.        
Application of a truncated cross-correlation function to signals received by the array may provide a correlation result that is less prone to error than is the case for conventional correlation functions. Moreover, the correlation can be achieved more quickly than is the case for conventional correlation functions. By carrying out the cross-correlation of the received signals in the time domain, the value of the interval is obtained directly.
Operation of a system according to this aspect can be contrasted with the operation of a phase comparison monopulse radar system. In such a system, a relationship between phase and frequency of received signals is first obtained. In many cases, this is done after mixing with a local oscillator. A delay is then calculated from the relationship between phase and frequency. However, it is recognised that such systems suffer from intrusion of phase noise that is inherent in many systems. Moreover, to preserve the unambiguous phase relationship, it is necessary for two receiving antennas to be placed closer together than the wavelength of the signal with the result that good angular resolution is possible with such systems only by providing several such spaced-apart antennas.
Conventional cross-correlation between two signals includes the step of summing the products of the two signals over a period (the interval of correlation) corresponding to the duration of the waveform contained in the signals. This step is carried out for a series of cases between which one of the signals is shifted in time with respect to the other over a range which, in conventional cross-correlation, is also comparable with the duration of the waveform.
In the first aspect, a truncated cross-correlation function is applied to the signals received by two or more of the receiving elements. By truncated cross-correlation it is preferably meant that the range over which one of the signals is shifted with respect to the other is less than that in conventional cross-correlation. Thus the truncated cross-correlation function is preferably operable to shift one output signal with respect to another over a range which is less than the duration of the signals and preferably less than the duration of a pulse.
The maximum time interval between receipt of the same signal at two receiving elements is equal to the time taken for the signal to propagate directly between them, which is equal to the distance between the elements divided by the speed of propagation of the transmitted signal. Therefore, it may be appropriate to limit the extent of cross-correlation to this time value, or to some related value. Thus the truncated cross-correlation function is preferably operable to shift one output signal with respect to another over a range in which the maximum offset in either direction is less than 5 times the time that would be taken for the transmitted signal to travel directly from one receiving element to another, and preferably less than or equal to 3, 2 or 1 times this value.
In this way, the amount by which a signal received by one of the receiving elements is shifted with respect to a signal received by another receiving element can be limited to a value corresponding, for example, to the maximum anticipated delay between the two. This may keep to a minimum the likelihood of false correlation peaks being generated and reduce the amount of processing required.
In certain circumstances it may be appropriate to limit the maximum offset to less than the time taken for the transmitted signal to travel directly from one receiving element to another. Such a situation may arise, for example, if the array has a field of view of less than 180°, in which case the maximum offsets may be reduced accordingly. The maximum positive offset and the maximum negative offset need not be equal, and indeed they may be different, for example if the field of view is not symmetrical.
In a typical embodiment, the signal has a characteristic wavelength λ and the interval of correlation (that is the range of signals used in the cross-correlation) is a small multiple of λ. For example, the interval of correlation may be less than 10, 5, or 2λ, or even 1λ. As a minimum, the cross-correlation function is applied over two samples, although in many embodiments a greater number of samples is used.
The interval of correlation may also (or alternatively) be related to the receiving elements. Specifically, where the receiving elements are spaced apart by a distance D (that is, the distance between adjacent receiving elements is D; however, the distance may also vary such that the D from a first receiving element to a second may be different than the D between either the first or second receiving element and any other receiving element), the truncated cross-correlation function may have an interval that is less than a small multiple of D. For example, the interval of correlation may be less than 5, 2, 1.5 or 1 D, or, where the detection field of at least one element is less than 180 degrees, it may be 0.9 D, 0.8 D or 0.7 D. This is a relevant consideration because the maximum difference in the length of the flight between the same signal received by two receiving elements is the spacing between those elements.
Typically the processing stage is operative to identify a maximum value of the cross correlation function. The maximum identifies the portions of greatest similarity between the two signals, and, from this, the interval between receipt of the two signals can be deduced.
Pulses preferably occupy a constant band of frequencies and are preferably relatively short.
The first aspect also provides apparatus for obtaining positional information relating to an object, optionally including any of the above mentioned features, the apparatus comprising:                transmitting means for transmitting a signal for at least partial reflection by the object;        a plurality of receiving means for receiving a signal reflected by the object; and        processing means for applying a truncated cross-correlation function to signals received by a plurality of the receiving means, thereby to determine a position of the object.        
In the first aspect there may also be provided, optionally in dependence of any apparatus described above, apparatus for obtaining positional information relating to an object in which the or a processing stage is operable to detect the interval between a signal being received by a first set of any two or more of the receiving elements and to determine a first angular position of an object from which the transmitted signal has been reflected; and to determine the interval between a signal being received by a second set (which may include one or more of the elements of the first set) of any two or more of the receiving elements and to determine a second angular position of an object from which the transmitted signal has been reflected; the processing stage being preferably operable by application of a truncated cross-correlation function.
In preferred embodiments, the first and second angular positions are measured in planes that are substantially non-parallel to one another. These angular positions can be used to provide two angular values of 3-dimensional polar co-ordinates of the object. Most favourable resolution of both angles can be achieved if the said planes are approximately normal to one another.
In an exemplary embodiment of the present apparatus, the processing stage may be operative to determine the distance from the array of an object from which a signal has been reflected. This can provide the third measurement required to obtain the co-ordinates of an object in three-dimensional space.
Thus, the three-dimensional position of an object may be determined with precision by measuring its angular position within what might be a relatively broad antenna beam, rather than using a larger antenna or a higher frequency to provide a precisely-tailored, narrow beam. This may permit the use of devices that have a smaller frequency/aperture ratio than has hitherto been possible.
The processing stage may be operable to determine a coordinate in three-dimensional space of an object from which the transmitted signal has been reflected, for example by using the angles determined as described in the last two preceding paragraphs.
In a favoured configuration, at least one of the first and second set of receiving elements includes three or more elements disposed such that that set includes at least two pairs of elements, the spacing of elements in the two pairs being unequal. This allows the same angular information to be obtained from two different pairs of receiving elements, to permit compensation for artefacts of the array, for example, grating lobes. For example, the spacing (D) between the elements of one pair may be approximately equal to (for example between 50% and 200% or between 75 and 150% of) a characteristic wavelength λ of the signal, the spacing between a second pair of elements may be approximately equal to 3λ/4, or 3 D/4, and the ratio of the spacing of the elements in one of the first and second pairs to the spacing of the elements in the other of the first and second pairs may be between 0.5 and 1 or 0.75 and 0.9. Preferably the relative spacing is arranged so that grating lobes which arise in the pairs line up differently, that is, a positive grating lobe for one pair substantially lines up with a negative or zero grating lobe for the other.
In embodiments according to the last-preceding paragraph, the processing stage may be operative to perform a truncated cross-correlation between the signals received by each pair of elements and to calculate the product of, or otherwise compare, the results of the cross-correlations. This can allow mutual calculation of errors or other artefacts in the received signals.
An apparatus in accordance with an exemplary embodiment may further comprise an output stage operative to generate an output for presentation of positional information relating to the object to a user. For example, the output may include at least one of an audible and a visual signal. The apparatus can thus be used to inform a user directly of the presence of an object in its field of detection.
Warning Zone
From a second aspect (which may optionally be provided in combination with the first aspect), an exemplary embodiment provides apparatus for obtaining positional information relating to an object, the apparatus comprising:                a warning zone definition stage for defining a warning zone (in two or three dimensions) within a detection field of the apparatus; and        a discrimination stage for determining whether a detected object is within the warning zone;        in which the warning zone is preferably defined as a three-dimensional region within the detection field.        
This aspect allows a warning zone to be defined that is largely independent of the shape of the beam generated by the transmitting element, that is, the antenna design can be decoupled from the zone definition. This can allow the system to operate at frequencies at which the beam formed by the antenna alone would be too wide, thereby allowing comparatively low frequency (and therefore low cost) apparatus to be used, and to use antennas which are smaller than would otherwise be applicable, and also less costly.
Preferably the apparatus further comprises an object location stage for determining the position of a detected object within the detection field of the apparatus. The discrimination stage may then be operable to compare the coordinates of the detected object to the coordinates of the warning zone to determine whether the object is within the warning zone. As will be seen, this arrangement acts to disconnect the function of generating a warning from detection of an object.
Typically, the warning zone may be contained within and may be smaller than the detection field of the apparatus. More specifically, the shape of the warning zone may be dissimilar from the shape of the detection field of the apparatus and/or may be non-circular or non-spherical. The shape of the warning zone may therefore be tailored to the needs of a particular application, largely independently of the shape of the detection field.
For example, the warning zone may include a region (such as a planar surface) defined in two dimensions within the detection field.
The warning zone definition stage may include an algorithm that defines a warning zone as a function of a coordinate within the detection field. Such a region may have an essentially arbitrary shape as defined by the algorithm. Alternatively or additionally, the warning zone definition stage may define at least a limiting value of one or more ordinates of a coordinate within the detection field. Each such limit effectively defines a cut-off of the warning zone in a particular direction. For example, the warning zone definition stage may define at least a limiting value of one or more angles of a polar coordinate within the detection field. Alternatively or additionally, the warning zone definition stage may define at least a limiting value of a range of a polar coordinate within the detection field. Such is the essentially arbitrary shape of a warning zone, that it may include a plurality of discontinuous spatial regions.
An exemplary apparatus according to an exemplary embodiment may further comprise an object location stage for determining the position of a detected object within the detection field of the apparatus. More specifically (or alternatively) the discrimination stage may include a coordinate generating stage that generates a coordinate of a detected object, which coordinate is then compared with the warning zone. In such embodiments, the discrimination stage is typically operable to determine the coordinates of the detected object and compare the determined coordinates with the coordinates of the warning zone to determine whether the object is within the warning zone.
In exemplary embodiments of this aspect, the discrimination stage may be operative to generate an output signal indicative that the object is within the warning zone. An apparatus embodying this aspect may be further operative to issue a warning, for example at least one of an audible, a visual or a tactile warning to a user upon detection of an object in the warning zone, thereby providing an immediate warning to a user.
As a development of this aspect, the warning zone definition stage defines a plurality of warning zones. The warning zones may be non-coextensive (overlapping, separated or spatially different) and/or alternatively defined, by which it is meant that different characteristics are used for determining whether an object is in the relevant warning zones. Thus the discrimination stage may be operable to apply different logic to at least two of the zones. For example, different zones may be provided for detecting different speeds or different sizes of objects. This can, for example, be used to provide warnings of multiple levels of severity, depending upon the position or other characteristics of a detected object.
An apparatus according to the last-preceding paragraph may be operative to generate an output signal indicative of which of the plurality of warning zones contains the object. For example, it may be further operative to issue at least one of an audible and a visual warning to a user upon detection of an object in a warning zone.
The warning zone may be limited in range and/or may be approximately cuboid.
In another development of this aspect of the apparatus, the discrimination stage is operative to analyse characteristics of objects outside of the warning zone. Such characteristics may be, for example, size of the object, distance of the object from the apparatus and/or the warning zone, direction of movement of the object relative to the apparatus and/or the warning zone, and relative speed of the object. As an example, the discrimination stage may be operative to track objects outside the warning zone and to predict their entry into the warning zone. The apparatus may be operative to issue a pre-warning based on the analysis.
For example, if the apparatus is mounted on a vehicle (as described below) in order to provide the driver with a parking aid, the apparatus may issue a pre-warning in the way described above if a large object is converging with the vehicle, even though that object may be outside of the warning zone. This may be particularly desirable, for example, if the object itself is heading for the vehicle in the same direction that the vehicle is heading for the object, which may give an increased risk of collision.
An apparatus embodying this or any other aspect may be suitable for use on a vehicle and may optionally include the vehicle. In such apparatus, at least one of the shape and a relevant dimension of a warning zone may at least in part be determined in dependence on a corresponding shape and dimension of the vehicle. For example, a warning zone may have a width that is equal to the width of the vehicle plus a predetermined amount (preferably which is less than the width of the vehicle) in order to assist an operator of the vehicle when navigating narrow openings. A warning zone may have a height that is equal to the height of the vehicle (including any accessories, such as a radio antenna) plus a predetermined amount (preferably which is less than the height of the vehicle), for example to allow for error and for suspension displacements. A warning zone may have a lower surface that is substantially planar and spaced above a road surface upon which the vehicle is supported. Spacing the lower surface above the road can exclude false alarms generated by low curbs, and small, insignificant objects on the road surface.
The shape and a relevant dimension of the warning zone of apparatus for use on a vehicle may be changed in response to vehicle operating conditions (by the warning zone definition stage). Such vehicle operating conditions may include at least one of speed, direction of travel, vehicle controls (such as accelerator, brake and clutch position) and ambient environmental conditions (amongst other possibilities). For example, the warning zone may extend further forward from the vehicle at high speed, and/or the zone may be extended further to one side of the vehicle when cornering.
Frequency Considerations
Typical exemplary embodiments in any aspect are operative to transmit an electromagnetic signal, typically radio frequency, for example, microwave, radiation. Such radiation is readily controllable and well-suited for the purposes of the exemplary embodiments.
For example, the transmitted signal may have a frequency of between 0.5 or 1 and 77 GHz, of between 2 and 25 GHz, of approximately one of 0.5 GHz, 1 GHz, 6 GHz, 10 GHz or 2–2.5 GHz. Such signals have a useful ability to penetrate solid objects, including objects made of wood, plastic material, concrete, brick and other non-metal materials. This might, for example, allow the apparatus to be located on the opposite side of a wall from a region that is to be monitored or within a structure of a vehicle such as a bumper. Moreover, such signals may be used to detect solid metal objects embedded within non-metal objects. These frequency ranges may be implemented using apparatus that is of advantageously low cost, and may have an advantageous ability to penetrate solid material. In a typical embodiment, the frequency may be approximately 2.45 GHz, possibly in order to meet applicable legislative requirements.
In general, a particular frequency will be chosen on the basis of several criteria: cost (low frequency is better), size of the antenna (high frequency is better), receiver performance (low frequency is better), scattering performance (this depends upon geometry, but a wide relative bandwidth (high bandwidth and low frequency) reduces glint), and applicable legislative requirements.
The transmitted signal may have a relative bandwidth (say, to the centre frequency) of approximately 15%, say between 3 and 33%, 5 and 25% or 10 and 20%.
An apparatus operating with a frequency and/or bandwidth set forth in the preceding paragraphs may be operative to resolve an angular position of an object with respect to a predetermined datum.
Pulse Length in Relation to Target/Array
From a third aspect (which may optionally be provided in combination with either or both preceding aspects or any other aspects), an exemplary embodiment provides apparatus for obtaining positional information relating to an object which is operative to transmit a signal into a detection field and to detect a signal reflected from an object in the detection field, in which the spatial length of the transmitted signal during its propagation is approximately the same as (say between 50 and 200% or 75 and 150%) a dimension of the smallest objects (for example, posts, rails, human limbs, vehicle components and equipment, furniture, aircraft components, etc.) that the apparatus is intended to resolve. This may help to ensure that a reliable correlation can be achieved between signals received at different receiving elements.
In order that the position of objects can be resolved to an accuracy of several centimeters, the spatial length of the transmitted signal during its propagation is preferably, in order of magnitude, not greater than, say, 1.0 m, 0.3 m, 0.1 m, 0.03 m or 0.01 m.
Two similar, closely spaced objects may give similar return signals. If these signals are one half wavelength out of phase with each other, or thereabouts, the two signals could interfere destructively, resulting in little or no signal. In order to reduce the risk of destructive interference, the wavelength of the transmitted signal is preferably not very much shorter than the spatial length, or, put another way, each pulse of the transmitted signal may comprise only a few wavelengths. For example, the spatial length of the transmitted signal during its propagation may be less than 10 wavelengths, or less than 6, 5, 3, 2 or even 1 wavelengths, although pulses of longer than any of these values may also be provided. By restricting the number of wavelengths per pulse, the likelihood of destructive interference occurring due to two closely spaced objects is reduced.
If the receiving elements are spaced too far apart then ambiguities may be introduced due to signals arriving at respective receiving elements with a delay shift of more than a half wavelength. On the other hand, if the receiving elements are too close together there may be insufficient angular resolution. Thus will be appreciated that the choice of distance between receiving elements is a trade off between achieving reasonable angular resolution by having a sufficiently large distance between the receiving elements, and avoiding ambiguity by having a sufficiently small distance between the receiving elements. In preferred embodiments, the signal is received at the apparatus at receiving elements spaced by a distance being of the same order of magnitude as a characteristic wavelength λ of the signal. For example, the receiving elements may be spaced apart by a distance nλ where n is a real number and 0.5≦n≦10, preferably 1≦n≦5.
Time Scale Adjustment/Stretching
In preferred embodiments, the signal generating stage applies a series of m pulses to the transmitting element to cause it to transmit a signal at times tn where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements; and                the detection stage detects a signal reflected to the receiving elements at times rn and generates an output signal representative of the received signal;        wherein the value of rn−tn varies as some function of n.        
By this arrangement, the flight time of a detected signal can be determined given only the knowledge of the value of n at which it was received and knowledge of the function of n.
For example, it may be that the value of rn−tn changes linearly with n, or it may vary in some other manner, for example in a pseudo-random sequence.
In a typical embodiment, the value of rn−tn increases or decreases linearly with n, by which it will be understood that the delay between a transmit time tn and a corresponding receive time rn increases or decreases linearly with n. Preferably, the delay varies from one pulse to an adjacent pulse; this can be a convenient way of putting the exemplary embodiments of the present system into practice. Although in one preferred embodiment the delay varies with each successive pulse, this is not necessarily the case; a first series of pulses at a first delay may be followed by a second series of pulses at a second, different, delay, and more than two different delays may be used. It will be appreciated that usually the delay is considered to be the delay with respect to the time at which the relevant pulse is transmitted.
Successive outputs of the detection stage may be stored in a storage means, the storage means being operable to output a signal of substantially the same shape as the received signal, but with a duration that is increased in time.
Preferably, in an exemplary embodiment of the present apparatus, the duration of each transmitted signal is less than the interval between transmitted signals. Most typically, the ratio between the duration of each transmitted signal and the mean interval between each transmitted signal is less than 1/10, for example less than 1/20 or 1/50, and greater than 1/1000, for example greater than 1/500 or 1/200.
Preferably, the detection stage is operable to detect the reflected signal during a detection aperture period, which is shorter than (preferably very much shorter than) the time between successive pulses. In this way, one or more (if a plurality of detection aperture periods is provided) so-called “range gates” may be provided, as described in WO97/14058; these might typically have widths corresponding to distances of between 1 and 2 cm. With the present apparatus, however, the range gates would move rather than, as in the prior art, remain stationary.
A timing stage may be provided to supplying timing signals to the detection stage and/or the signal generating stage. Preferably, the timing stage is adapted to operate the detection stage by means of a timing pulse. A timing pulse (or pulses) is an efficient way to generate the range gate (or gates).
Preferably, a plurality of spaced receiving elements is provided. With a sufficient number of elements a precise location of the object in space can be determined. Moreover, if as is preferred the transmitting elements have a wide beam and little individual angular resolution, sufficient elements can be provided so that the angular position of objects can be determined by trilateration; that is, by precise path-length comparison.
Preferably the apparatus further comprises a computation stage for processing signals detected by the detection stage, determining the time interval between a single reflected signal arriving at a plurality of the receiving elements, and thereby obtaining positional information relating to the object from which the signals were reflected.
The signal generating means preferably operates in an operation cycle to generate a sequence of spaced pulses simultaneously with or at a fixed time after each of a plurality of transmitting trigger instants. The detection stage may be adapted to detect the signals from the receiving elements simultaneously with or at a fixed time after each of a plurality of receiving trigger instants, each of which occurs at a time in predetermined relation to the transmitting trigger instants. For example, for each transmitting trigger instant tn, a corresponding receiving trigger instant may occur at rn, the time interval rn−tn being a predetermined function of n. In such a system, the interval rn−tn may be a function of the general form of T0+nT where T0 and T are constants and n=1, 2 . . . m.
Preferably the value of t/T (that is, the ratio between the mean interval between transmit trigger instants and the increment in the delay between transmit and receive trigger instants) is of several orders of magnitude; for example, t/T may be between 103 and 107, or between 104 and 106, typically about 105.
By arranging the value of rn−tn to increase (or decrease) as a function of n the received signals may be stretched in the time domain by a factor of t/T, as will now be explained.
The output of the detection stage may be fed to a storage means, such as a capacitor or a sample and hold stage, which stores the value of the signal which is received at each receiving trigger instant rn. The signal received at a receiving trigger instant rn may thus be stored until the next receiving trigger instant rn+1 (that is, the signal is sampled and held at each receiving trigger instant) Since each receiving trigger instant has a slight increment T in the delay from the corresponding transmit trigger instant, the value of the signal stored by the storage means changes with each new trigger instant. It therefore takes t/T repetitions to complete the waveform.
Assuming that the reflected signal is essentially unchanged between trigger instants (such as is the case if the object does not move significantly relative to the transmitting and receiving elements), then a strobe effect takes place which results in the detected signal being stretched by a factor of t/T. In this way the output of the storage means may be of duration greater than that of the received signals by a factor t/T and of frequency less than that of the received signals by a factor t/T.
The last-described arrangement can stretch the received signal in time without changing the signal shape. This is beneficial because it can reduce by a factor of t/T the frequency at which the computation stage can operate. The value of t/T may be considered as a constant divisor of frequency and multiple of time. This allows processing of signals output from the detection stage to take place at a frequency substantially less than the frequency of the received signal, with a consequent advantage in complexity and cost of processing apparatus.
Thus the apparatus may further comprise a storage means for storing values of the output signal corresponding to signals received at times rn. The storage means may be operable to output a signal of substantially the same shape as the received signal, but with a duration which is increased in time (by a factor of t/T).
Sampling Stage/Single Control Line
An apparatus in accordance with an exemplary embodiment may include a sampling stage operative under the control of the timing stage selectively to pass or to interrupt the passage of signals from the receiving elements to the detection stage. The sampling stage may pass signals to the detection stage for an aperture time ta.
Typically, such apparatus comprises a respective sampling stage for each receiving element. Advantageously, each sampling stage is connected to the timing stage by a respective signal delay line, within which delay line a signal is delayed by a time not less than ta/2. This ensures that signals cannot travel from one sampling stage to another through the timing stage during the aperture time, thereby minimising crosstalk between the sampling stages.
To facilitate processing of the received signals, the detection stage typically includes an analogue to digital conversion stage such that the output of the detection stage is a digital signal. The output of the detection stage advantageously includes an indication of the amplitude of the received signals.
From a further aspect, an exemplary embodiment provides apparatus for obtaining positional information relating to an object according to any preceding claim, contained within a single housing. Such apparatus may be hand-holdable in use. For example, the apparatus may be intended to provide information about the location of objects within a wall.
Advantageously, an apparatus may comprise an antenna array and processing means constructed as a single assembly. In such embodiments, the processing means operates to provide all functional electrical signals to and receive all functional electrical signals from the array.
An apparatus in accordance with an exemplary embodiment may be intended for use in a vehicle.
Angle Measurement in Vehicle Radar
Apparatus for obtaining positional information relating to an object, according to any aspect, is advantageously contained within a single housing. Such apparatus may be particularly for use in a land vehicle. This may greatly simplify its installation, for example, in a vehicle. Such apparatus may alternatively be hand-holdable for use. This is of particular application in cases where the apparatus is embodied in a hand-held tool, such as a device for obtaining information about objects within a wall.
This feature may be provided independently. Accordingly there is apparatus for obtaining positional information relating to an object which is advantageously contained within a single housing. Such apparatus may be particularly for use in a land vehicle. This may greatly simplify its installation, for example, in a vehicle. Such apparatus may alternatively be hand-holdable for use. This is of particular application in cases where the apparatus is embodied in a hand-held tool, such as a device for obtaining information about objects within a wall.
From a fifth aspect (which may optionally be provided in any combination with any other aspect), an exemplary embodiment provides an apparatus for obtaining positional information relating to an object, for use on a vehicle, for resolving the angular position of an object preferably using non-Doppler radar.
There may also be provided with any aspect, particularly for a land vehicle, for obtaining positional information relating to an object, apparatus for comprising:                means for transmitting a probe signal towards the object;        means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object; and        detecting means, coupled to the receiving means, for detecting the relative timing of the returned probe signals as received at the plurality of locations;        whereby the positional information for the object can be determined from said relative timing.        
Apparatus, particularly for a land vehicle, for obtaining positional information relating to an object, embodying any combination of aspects for use on a vehicle may be for obtaining positional information relating to an object external of or internal to the vehicle, the apparatus being operative to generate 3-dimensional positional data for the object. This can, for example, provide an operator of the vehicle with a warning of an obstruction risk, or it may override controls of the vehicle.
Alternatively or additionally, apparatus embodying any combination of aspects for use on a vehicle may be for obtaining positional information relating to an object internal to the vehicle, the apparatus being operative to generate 3-dimensional positional data for the object. Typically, such apparatus has a detection field within a passenger compartment of the vehicle.
In apparatus according to any of the last three preceding paragraphs, the positional data may include at least one of the range, azimuth and elevation of the object.
Most typically, the antenna array of an exemplary embodiment for use on a vehicle is carried on a fixed location on the vehicle. Advantageously, the antenna array is located within a component of the vehicle, preferably a non-metallic component. Thus, visual conflict with the styling of the vehicle can be avoided and the array can be protected. For example, the antenna array may be located within a bumper (or other portable enclosure) of the vehicle, such as a (preferably a non-metallic) bumper, from which it can generate a detection zone to the front or to the rear of the vehicle.
In (for example) a vehicle installation, an exemplary embodiment of the present apparatus may further comprise alerting apparatus for alerting a vehicle driver to the presence of a detected object. Such apparatus may provide to the driver (or another person, or a user of the apparatus, as the case may be) information that would otherwise be unavailable.
In such embodiments, the alerting apparatus is operative to generate an audible warning, which, for example, may include a verbal warning that may convey information about detected object(s). Alternatively or additionally, the alerting apparatus may be operative to generate a visual warning. For example, the visual warning may include a visible representation (an image) of the position of an object detected by the apparatus.
An exemplary embodiment of the present apparatus may further comprise a display upon which is presented a visual representation e.g. an image of a detection field of the apparatus and an object within the detection field.
Imaging/Pattern Matching
From a sixth aspect (which may optionally be provided in any combination with any other aspect), an exemplary embodiment provides an apparatus for obtaining positional information relating to an object, for use on a vehicle, preferably using non-Doppler radar and being operative to determine a radar cross-section of an object.
From a seventh aspect (which may optionally be provided in any combination with any other aspect), an exemplary embodiment provides an apparatus, particularly for use on a (for example land) vehicle, for obtaining positional information relating to an object, including a transmitting element for transmitting radiation into a detection field, a receiving element for receiving radiation reflected from an object in the detection field, and a processing stage, which is operative to analyse the signals from the receiving element to derive qualitative information relating to the object. This permits the apparatus to provide extended data relating to objects that it detects.
For example, the processing stage may be operative to compare information relating to an object at successive different angular positions against a look-up table. This allows variation in the gain of the antenna array with angle to be accounted for.
The processing stage may be operative to determine a radar cross-section of the object. In such embodiments, the processing stage may be operative to compare the radar cross section with a threshold value of radar cross-section and to generate a warning signal in dependence upon the result of the comparison.
Alternatively or additionally, the processing stage may be operative to determine an evolution of angular position of an object with time. In one example, the processing stage is operative to determine the rate of change of angular position of the object. In another example, the way in which the angular position evolves with time is determined. By determining not just the rate of change of angular position, but also how the angular position varies with time, the accuracy with which the relative movement of the vehicle and the object can be predicted is increased.
For example, if the vehicle is moving towards a curb which is below the level of the sensor, the vertical angular position of the curb will change as a hyperbola as the vehicle moves towards and over the curb. By defining the characteristic hyperbola, the movement of the vehicle relative to the curb can be predicted. In this way, it can be predicted whether the vehicle will hit the curb or not, and by how much the vehicle will miss the curb.
In another example, if the vehicle is moving towards an object, such as a post, which is not directly in the line of travel, then the horizontal angular position of the object will change as a hyperbola as the vehicle moves towards and past the object. By defining the characteristic hyperbola, it can be predicted whether or not the vehicle will hit the object, and by how much.
In a further example, if, as the vehicle moves, a target not on the centre line maintains a constant angular position as the vehicle moves, this may indicate a hazard such as a moped which is moving alongside the vehicle at the same speed.
The above situations may be also be analysed by considering how the distance away from the object changes as a function of distance moved by the vehicle. For example, if the distance away from an object changes as a straight line against distance moved by the vehicle then it may be predicted that the vehicle will hit the object, and the point of collision may be predicted by extrapolating the line. If the distance away from the object changes as a curve against distance moved, then it may be predicted that the vehicle will miss the object. The amount by which the vehicle will miss the object, and the point at which the object will be closest to the vehicle, may be predicted by estimating the evolution of the curve.
Thus the processing stage may be operative to predict a path of movement of the object, preferably relative to the apparatus.
If the evolution of the angular position of the object differs from that which would be produced by a point object, then it may be inferred that the object has an irregular outline, and the outline of the object may be predicted based on the difference. For example, if the vehicle is moving towards an object (such as another vehicle) with a curvilinear outline, the radar may see the nearest point of the object, but not the part of the object closest to the path of the vehicle. By predicting the outline of the object, it can be predicted where the vehicle will hit the object, even if that part of the object is not yet visible.
An exemplary embodiment further provides apparatus for obtaining positional information relating to an object substantially as herein described with reference to the accompanying drawings.
Applications
From an eighth aspect, an exemplary embodiment provides a vehicle equipped with apparatus embodying any of the above-mentioned aspects.
More specifically, an exemplary embodiment may provide a (preferably motor) road vehicle being equipped with a driver warning system comprising apparatus embodying any of the above-mentioned aspects for obtaining positional information relating to an object external of the vehicle, the apparatus being operative to generate 3-dimensional positional data for the object. In such a vehicle, the array of the apparatus may be contained within a non-metallic bumper of the vehicle.
A vehicle embodying this aspect of the exemplary embodiment may comprise a display instrument operative to process information obtained by the apparatus and to generate a display therefrom for an operator of the vehicle.
From a ninth aspect, an exemplary embodiment provides a control system for air bags in a vehicle, the control system comprising an exemplary embodiment of the present apparatus, in which the processing stage is operable to determine the occupancy of a seat equipped with a passenger air bag, and to suppress deployment of the bag in dependence on the occupancy of the seat. For example, the processing stage may be operable to determine whether or not the seat is occupied and to suppress deployment of the bag if the seat is unoccupied, and/or to determine if the occupant is too close to the air bag (such that release of the air bag would represent a hazard to the occupant) and to suppress deployment of the bag if the occupant is too close.
This exemplary embodiment also provides embodiments being hand-held tools and devices for obtaining information about objects within a wall comprising a apparatus according to any of the preceding aspects.
Antenna Array
From a tenth aspect, an exemplary embodiment provides an electromagnetic (for example, microwave) antenna array optionally for use in combination with any other aspect, the array including a transmitting element and a plurality of receiving elements, the transmitting and receiving elements being disposed on a common substrate.
This feature of the exemplary embodiment may be provided independently. Accordingly the exemplary embodiment provides an electromagnetic (for example, microwave) antenna array, the array including a transmitting element and a plurality of receiving elements, the transmitting and receiving elements being disposed on a common substrate.
An electromagnetic antenna array embodying this aspect may include a single transmitting element, or a plurality of transmitting elements.
An electromagnetic antenna array embodying this aspect may include three (or more) receiving elements arranged non-collinearly. For example, the receiving elements are arranged substantially at the vertices of a right-angled triangular locus (that is, in an L-shaped pattern).
In one exemplary embodiment there is an electromagnetic antenna array optionally for use in apparatus for obtaining positional information relating to an object, the array including a transmitting element and at least three receiving elements arranged non-collinearly, the transmitting and receiving elements being disposed on a common substrate.
The receiving elements may be spaced apart by a distance that is the same order of magnitude as the wavelength λ of the radiation that it is intended to transmit and receive. For example, the receiving elements may be spaced apart by a distance mλ where m is less than 10, and preferably less than 8, 5, 3 or 2, and m is greater than 0.1, and preferably greater than 0.2, 0.3, or 0.5.
The efficiency with which the elements can radiate or detect radiation decreases as the size of the elements decreases, since the radiation impedance of the elements may decrease with size, and thus the elements themselves should not be too small. On the other hand, the elements should not be too large, because they may become physically too big for the array, and because grating lobe effects may occur at larger sizes. In general, the size of the elements (whether receiving or transmitting) is preferably less than 10λ or 4λ and greater than about λ/4. In preferred embodiments, the size is in the region of λ/4 or λ/2, although other values may be used. In one particular example, the elements have a size of about 1.5 cm with a wavelength of about 5 cm.
More advantageously, an electromagnetic antenna array according to the present aspect may include four receiving elements arranged non-collinearly. For example, the receiving elements may be arranged substantially at the vertices of a quadrilateral locus, more specifically, a trapezoidal or rectangular locus, in which the quadrilateral has long and short parallel sides.
In accordance with this aspect the electromagnetic antenna array may include at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.
This feature may be provided independently. Accordingly there is an electromagnetic antenna array including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.
In embodiments where the locus is a trapezium (that is, a quadrilateral having only two sides parallel), this arrangement can ensure that two unequally-spaced pairs of antennas in parallel planes can be selected, with dissimilar artefacts (for example, grating lobes) in their sensitivity patterns. Advantageously, the short side may be between 0.5 and 1 times (or approximately three-quarters of) the length of the long side. As a specific example, where the trapezial locus has long and short parallel sides, the length of the shorter side being approximately the wavelength λ of the radiation that the array is intended to transmit and receive, and the length of the longer side is approximately 3λ/2. By suitable processing of signals from such an array, the effect of grating lobes can be substantially reduced.
Alternatively, the quadrilateral may have two opposing angles which are substantially right angles, while the other two angles are not right angles. This arrangement can ensure that the main grating lobe for each will point in the correct 3-D direction, while the artefacts will be different, and thus will cancel out.
More generally, to achieve the advantages discussed in the last-preceding paragraph, the exemplary embodiment may provide a microwave antenna array for use in apparatus for obtaining positional information relating to an object, which apparatus may be in accordance with any other aspect, the array including a transmitting element and a plurality of receiving elements, in which the spacing of two pairs of (the) receiving elements in a common direction is unequal. This can be achieved in a wide range of embodiments, including that discussed above.
Further Aspects
From an eleventh aspect, an exemplary embodiment provides an electromagnetic sensor for use on a vehicle, whether ground-, water- or air-borne, contained in a single enclosure, comprising timing control means, transmitting means, receiving means, processing means and interface means, in which:                said transmitting means includes a fixed antenna capable of emitting a sequence of short pulses of electromagnetic radiation in the ultra-high-frequency microwave or millimeter wave band in response to trigger signals from said timing means into a field of view in excess of +/−15 degrees in width and +/−10 degrees in height from a pointing direction of the antenna,        said receiving means is responsive to further trigger signals from said timing means and includes one or more fixed receive antennas responsive to signals corresponding to received fractions of such pulses after transmission, propagation to and scattering from one or more obstacles within such field of view, adapted to convert such signals to signal information in which each frequency component of such signal is converted to a respective component of such signal information at a frequency related to such frequency component by a constant divisor for all such respective frequency components,        said processing means is adapted to acquire said signal information thus responsive to said received fractions at each of said receive antennas and calculate information concerning said obstacles,        said interface means are adapted to communicate either to a user of said vehicle or to other electronics systems on the vehicle, which is adapted to measure and provide via such interface means indications of the presence or absence of one or more obstacles within a volume which is not coextensive with the field of view of said antennas and can be defined independently of such field of view.        
In a sensor according to the last-preceding paragraph the processing means may be adapted to provide via such interface means information concerning the distances, azimuth angles and elevation angles from said sensor to said one or more obstacles.
In a sensor embodying this aspect, the said volume may be contained within one or more surfaces, such as a plurality of effectively planar surfaces. The processing means may also be adapted to provide via such interface means indications of the reflecting strength of the obstacle, proportional to its radar cross section, and independent of its distance or position in the field of view of the sensor.
In typical embodiments the antenna array is fixed with respect to its mounting; that is to say, it does not rotate.
A preferred embodiment of sensor according to this aspect is adapted to fit within a bumper (or other portable enclosure) of a vehicle, or within a handheld tool or enclosure.
From a further aspect, the exemplary embodiment provides apparatus for obtaining positional information relating to one or more objects, the apparatus being operative in an operating cycle for each of m steps in which n=1, 2 . . . m, the apparatus including:                a signal generating stage operative, simultaneously with or at a fixed time after a transmitting trigger instant tn to generate a signal, and a transmitting element to transmit said signal into a detection field;        a plurality of spaced receiving elements operative simultaneously with or at a fixed time after a receiving trigger instant rn to receive a portion of the signal reflected from one or more objects in the detection field, the interval rn−tn varying as a function of n and having a magnitude in a range corresponding to the times of travel of a signal reflected from an object within the detection field;        means for identifying the values of n at which signals reflected from one object are received at two or more receiving elements and thereby detecting the time taken, and therefore the distance travelled, by the signals from the transmitting element to the various receiving elements; and        means for calculating the position of the object from the various path lengths thereby identified.        
In an electromagnetic imaging sensor according to this aspect, the transmitting and/or the receiving means are embodied in a single microchip, with the associated antenna elements printed on one or more adjacent printed circuit cards, and the timing signal generator means and control and processing means are embodied in the same single microchip. The transmitting means may comprise a semiconductor switching device or amplifier external to the said single microchip. Moreover, the receiving means may comprise one or more semiconductor switching devices or amplifiers external to the single microchip. More specifically, both transmitting and receiving means may comprise external semiconductor switching devices or amplifiers, and the timing signal generator and control and processing means are embodied in a single microchip. Yet more specifically, both transmitting and receiving means comprise semiconductor switching devices or amplifiers, and the timing signal generator and control and processing means may be embodied in two separate microchips.
Receiving means of embodiments of this aspect may comprise switching samplers in which the switch may be closed for an aperture time less than or comparable with one half the period of said dominant period. In such embodiments, the switches may all be closed by a common signal without intervening pulse generating circuits. Advantageously, the switching amplifiers may be electrically separated by lengths of transmission line whose electrical length exceeds or is comparable to one half the duration of said aperture time.
The antennas in this aspect may be stacked microstrip patches. Suitably, the stacked microstrip patches may be fed by slots in the circuit card carrying the transmitting means.
The delay measurement process may, in preferred embodiments, include a cross-correlation process. Such a correlation process may be a truncated correlation process in which the range of the correlation is calculated between the signals received by any two elements is related to the spatial separation of those two elements. For example, the delay measurement process comprises measurement of the timing difference between comparable features of the waveform such as zero-crossings, peaks, troughs, etc.
The control and processing means of this aspect may also comprise classification means to identify classes of object near to a vehicle by pattern matching with said image.
The said distance and said angular position of each said object may be used to identify the positions of a plurality of said objects in two or three dimensions. The positions of said plurality of said objects may be combined to form an image of the contents of the space near or in front of the sensor.
In embodiments of this aspect, the control and processing means may comprise or may be connected to further processing means in which successive such images or the signals from which they were generated are used in a synthetic aperture or inverse synthetic aperture process to further detail the image of the contents of the space near or in front of the sensor. Such an imaging sensor may store digitally a description of a volume of space near the antenna. The volume of space may be other than a sphere or ellipsoid. Moreover, the measured position of each such object may be compared with such volume of space near the antenna to determine its location inside or outside such volume.
The processing means may store a description of the gains of the antennas as a function of solid angle. The measured position of each object may be used with such description of the gains to determine the gain of each of the antennas in that direction. In such embodiments (and others), the measured signal strength arising for each object may be divided by the product of the antenna gains corresponding to its position and multiplied by the fourth power of the measured range to provide a value proportional to its radar cross-section. For example, the derived value of radar cross-section may be compared with a cross-section threshold to determine the significance of the target. The cross-section threshold may be divided by the fourth power of the measured range and multiplied by the product of the antenna gains in the direction of the object before comparison with the measured signal strength.
Exemplary embodiments also provide apparatus according to any of the above-defined aspects for generating an image of objects within or through a solid object. Typically, the solid object may be a wall.
Further exemplary embodiments provide apparatus according to any of the above-defined aspects for providing an image of an environment in conditions that human vision is compromised. For instance, vision may be compromised by the physiological condition of a user (such as a physical handicap). Alternatively, vision may be compromised by environmental conditions, such as darkness, smoke or fog.
Method Aspects
Angular Resolution by Cross-Correlation
From a first method aspect provides a method for obtaining positional information relating to an object, optionally in apparatus in accordance with any one of the preceding aspects, comprising:                applying a series of pulses to a transmitting element of an array to cause it to transmit a signal, such that at least a portion of the signal is reflected from the object to be received by the receiving elements;        detecting signals reflected to receiving elements of the array and generating output signals representative of the received signals; and        applying a truncated cross-correlation function to the output signals to detect the interval between signals received by a plurality of the receiving elements, whereby to determine an angular position of an object from which the transmitted signal has been reflected.        
Preferably the truncated cross-correlation function comprises shifting one output signal with respect to another over a range which is less than the duration of the signals and preferably less than the duration of a pulse. For example, the truncated cross-correlation function may comprise shifting one output signal with respect to another over a range in which the maximum offset in either direction is less than 5 times the time that would be taken for the transmitted signal to travel directly from one receiving element to another, and preferably less than or equal to 3, 2 or 1 times this value.
The signal may have a characteristic wavelength λ and the truncated cross-correlation function may have an interval of correlation which is a small multiple of λ. For example, the interval of correlation may be less than 10, 5, or 2λ, or even λ. As a minimum, the cross-correlation function is applied over two samples, although preferably a greater number of samples is used.
In a method embodying this aspect in which the receiving elements are spaced apart by a distance D, the truncated cross-correlation function may have an interval that is less than a small multiple of D. The interval of correlation may be less than 5, 2, 1.5 or 1 D.
Such a method may further include determining the distance from the array of an object from which a signal has been reflected. This can, for example, be achieved by multiplying the time taken for the signal to be received by the speed of propagation of the signal. Typically, a maximum value of the cross correlation function is identified.
A method in accordance with an exemplary embodiment may further include a step of determining the distance from the array of an object from which a signal has been reflected. This may be achieved by multiplying the time taken for the signal to be received by the speed of propagation of the signal.
The first method aspect also provides a method of obtaining positional information relating to an object, optionally including any of the above mentioned features, the method comprising:                transmitting a signal for at least partial reflection by the object;        receiving signals reflected by the object; and        applying a truncated cross-correlation function to received signals, thereby to determine a position of the object.        
In the simplest case the signals are received by two receiving elements and the interval between signals received by those two receiving elements is determined. If more than two receiving elements are provided, a truncated cross-correlation function may be applied to some or all of the various pairs of received signals, such that a plurality of angular positions are determined. In this way the accuracy of the measurement may be improved and/or another dimension added to the measurement.
Thus, a method embodying this aspect may include the steps of:                determining the interval between a signal being received by a first set of any two or more of the receiving elements;        calculating a first angular position of an object from which the transmitted signal has been reflected;        determining the interval between a signal being received by a second set of any two or more of the receiving elements (which may include one or more of the elements of the first set); and        calculating a second angular position of an object from which the transmitted signal has been reflected.        
Preferably, the first and second angular positions are measured in planes that are substantially non-parallel to one another, and more optionally, the said planes are approximately normal to one another.
The method may include determining a coordinate in three-dimensional space of an object from which the transmitted signal has been reflected.
In a method in accordance with an exemplary embodiment at least one of the first and second set of receiving elements includes three or more elements which may be disposed such that that set includes at least two pairs of elements, the spacing of elements in the two pairs being unequal. In an advantageous embodiment, the spacing (D) between the elements of one pair is approximately equal to (for example between 50% and 200% or between 75 and 150% of) a characteristic wavelength λ of the signal, and preferably the spacing between a second pair of elements is approximately equal to 3λ/4, or 3 D/4, and preferably the ratio of the spacing of the elements in one of the first and second pairs to the spacing of the elements in the other of the first and second pairs is between 0.5 and 1 or 0.75 and 0.9. In such embodiments, a truncated cross-correlation may be performed between the signals received by each pair of elements and the product of the result of the cross-correlations may be determined.
A method in accordance with an exemplary embodiment of the present apparatus may further comprise generating an output for presentation of positional information relating to the object to a user. The output may include at least one of an audible and a visual signal.
Warning Zone
From a second method aspect, an exemplary embodiment provides a method for obtaining positional information relating to an object, optionally in combination with the first aspect, comprising:                defining a warning zone within a detection field; and        determining whether a detected object is within the warning zone:        wherein the warning zone is preferably defined as a three-dimensional region within the detection field.        
Typically, the warning zone is contained within and is smaller than the detection field. Moreover, the shape of the warning zone may be dissimilar from the shape of (and/or may be smaller than) the detection field. Preferably the method includes the step of determining the position of a detected object within a detection field.
The warning zone may include a region defined in two dimensions within the detection field. For example, the warning zone may be a planar surface within the detection field. Alternatively, the warning zone may be defined as a three-dimensional region within the detection field.
The warning zone may be defined by an algorithm as a function of a coordinate within the detection field. Alternatively or additionally, the warning zone may be defined by at least a limiting value of one or more ordinates of a coordinate within the detection field. For example, the warning zone may be defined by at least a limiting value of one or more angles of a polar coordinate within the detection field. Moreover, the warning zone may be defined by at least a limiting value of a range of a polar coordinate within the detection field. The warning zone may include a plurality of discontinuous spatial regions.
A preferred method according to this aspect further includes generation of a co-ordinate of a detected object. In such a method, the generated co-ordinates may be compared with co-ordinates of the warning zone to determine whether the object is within the warning zone.
A method in accordance with an exemplary embodiment may further comprise the step of generating an output signal indicative that the object is within the warning zone. Typically, the method further comprises the step of issuing a warning to a user upon detection of an object in the warning zone.
In a modification to a method in accordance with an exemplary embodiment, there is defined a plurality of non-coextensive warning zones. In such embodiments, there may be included a step of generating an output signal indicative of which of the plurality of warning zones contains the object.
In another development of this aspect the method may further comprise the step of analysing a characteristic of an object outside of the warning zone. The step of analysing a characteristic may comprise tracking an object outside the warning zone and predicting its entry into the warning zone.
Typical methods embodying the exemplary embodiment further comprise a step of issuing at least one of an audible and a visual warning to a user upon detection of an object in a warning zone.
A method embodying this aspect may be carried out on a vehicle. In such methods, at least one of the shape and a relevant dimension of a warning zone may be at least in part determined by a corresponding shape and dimension of the vehicle.
A method as set forth in the last-preceding paragraph typically includes monitoring operating conditions of the vehicle and changing at least one of the shape and a relevant dimension of the warning zone in response to vehicle operating conditions. Such operating conditions my include (amongst other possibilities) at least one of speed, direction of travel, and ambient environmental conditions. For example, the distance to which the warning zone extends in the direction of travel of the vehicle may be increased with the speed of the vehicle. Alternatively or additionally, the extent to which the warning zone extends to one side of a longitudinal axis of the vehicle may be increased in a direction in which the vehicle is turning.
Frequency Considerations
In a method embodying an exemplary embodiment, the signal is most typically an electromagnetic signal. More specifically, in a method embodying the exemplary embodiment, the electromagnetic signal is most typically microwave radiation. For example, the electromagnetic signal may have a frequency of between 0.5 or 1 and 77 GHz, of between 2 and 25 GHz, or it may be approximately one of 0.5 GHz, 1 GHz, 6 GHz, 10 GHz or 2–2.5 GHz. For example, the frequency of the electromagnetic signal may be approximately 2.45 GHz. The transmitted signal may typically have a relative bandwidth (say, to centre frequency) of approximately 15%, preferably between 3 and 30%, 5 and 25%, or 10 and 20%. The transmitted signal may have a relative bandwidth to the centre frequency between 10 and 20%, between 5 and 25%, between 3 and 33% or approximately 15%.
In a method embodying any of the last three preceding paragraphs, an angular position of an object may be resolved with respect to a predetermined datum.
From a third method aspect, an exemplary embodiment provides a method of obtaining positional information relating to an object, optionally in combination with any of the other method aspects, comprising transmitting a signal into a detection field and detecting a signal reflected from an object in the detection field, in which the spatial length of the transmitted signal during its propagation is approximately the same as a dimension of the smallest object that the apparatus is intended to resolve.
In such a method, the spatial length of the transmitted signal during its propagation may be, in order of magnitude, not greater than say, 1.0 m, 0.3 m, 0.1 m, 0.03 m or 0.01 m. For example, the spatial length of the transmitted signal during its propagation may be less than 10 wavelengths, or less than 6, 5, 3, 2 or even 1 wavelengths.
Typically, in a method embodying this aspect, the signal is received at receiving elements spaced by a distance being of the same order of magnitude as a characteristic wavelength λ of the signal. More specifically, the receiving elements may be spaced apart by a distance nλ where 0.5≦n≦10, or 1≦n≦5.
Time Scale Adjustment/Stretching
A method embodying this aspect may include                a series of pulses comprises m pulses to cause the transmitting element to transmit a signal, at times tn where n=1, 2 . . . m; and        reflected signals are detected by the receiving elements at times rn; comprising the steps of        generating an output signal representative of the received signal; wherein the value of rn−tn varies as some function of n.        
In preferred embodiments of a method embodying this aspect, the value of rn−tn changes linearly with n. Alternatively, it may vary in some other manner, for example in a pseudo-random sequence.
Preferably the method further comprises storing values of the output signal corresponding to signals received at times rn. The method may further comprise outputting a signal of substantially the same shape as the received signal, but with a duration which is increased in time. For example, the duration may be increased by several orders of magnitude, for example, by between 103 and 107, or between 104 and 106.
Angle Measurement in Vehicle Radar
From a fourth method aspect, an exemplary embodiment provides a method for obtaining positional information relating to an object, performed on a vehicle optionally in combination with any other method aspect, for resolving the angular position of an object using non-Doppler radar.
A method in accordance with an exemplary embodiment may be performed on a vehicle for obtaining positional information relating to an object external of the vehicle, in which 3-dimensional positional data for the object is generated.
A method in accordance with an exemplary embodiment may be performed on a vehicle for obtaining positional information relating to an object internal to the vehicle, in which 3-dimensional positional data for the object is generated. In a method embodying the exemplary embodiment, a detection field may be within a passenger compartment of the vehicle.
Positional data obtained by a method embodying the exemplary embodiment may include at least one of the range, azimuth and elevation of the object.
A method in accordance with an exemplary embodiment may be carried out by apparatus including an antenna array that is carried on a fixed location on the vehicle. Such an antenna array may be located within a (preferably non-metallic) component of the vehicle. For example, the antenna array may be located within a (preferably non-metallic) bumper of the vehicle.
A method in accordance with an exemplary embodiment may further comprise a step of alerting a vehicle driver to the presence of a detected object. In such embodiments, the alerting step may include generating an audible warning. The audible warning may, for example, include a descriptive verbal warning. Alternatively or additionally, the alerting step may include generating a visual warning. The visual warning may include a visual representation (an image) of the position of detected objects. Such a method may further comprise a step of presenting a visual representation of a detection field and objects within the detection field.
Imaging/Pattern Matching
From a fifth method aspect, an exemplary embodiment provides a method for obtaining positional information relating to an object, performed on a vehicle optionally in accordance with any other method aspect, using non-Doppler radar, the method including determining a radar cross-section of a object.
From a sixth method aspect, an exemplary embodiment provides a method for obtaining positional information relating to an object, optionally in accordance with any other method aspect, including transmitting radiation into a detection field, receiving radiation reflected from an object in the detection field, and in an analysis step analysing the signals from the receiving element to derive qualitative information relating to the object.
In a method embodying this aspect, a radar cross-section of the object may be determined. The radar cross section may be compared with a threshold value of radar cross-section and a warning signal may be issued in dependence upon the result of the comparison. Alternatively or additionally, in such a method, an evolution of angular position of an object may be determined, and/or a path of movement of the object may be predicted.
In the analysis step of a method embodying this aspect, the signals may be modified to compensate for angular variation in sensitivity of the receiving element. Moreover, in the analysis step the signals may be modified to account for the range of the object from which the signals are reflected.
In a method embodying this aspect, the analysis step may include making a comparison between the received signal and a pattern corresponding to signals received from a known class of objects. Such an analysis may include identification of characteristic features of the received signals. The characteristic features may include at least one of minima, maxima and zero-crossings.
This exemplary embodiment also provides a method for obtaining positional information relating to an object substantially as herein described with reference to the accompanying drawings.
From another aspect, an exemplary embodiment provides a method of controlling deployment of air bags in a vehicle, in which a method according to any other method aspect is applied to determine the occupancy of a seat equipped with a passenger air bag, and deployment of the bag is suppressed in dependence on the occupancy of the seat, for example, if the seat is unoccupied or if the occupant is too close to the air bag.
A portion of the signal emitted from the transmitting element will propagate directly to the receiving elements without being reflected off an object in the detection field. This will be detected at the receiving elements a very short time after the transmitting trigger instant with the result that the ability of the apparatus to resolve objects at short range may be limited. The receiving elements may be disposed in a symmetrical relationship with the transmitting element whereby such signals will be detected by the receiving elements substantially simultaneously and with a substantially similar signal shape. This arrangement can simplify the processing required to compensate for the existence of these signals. However, in some circumstances the best results may be obtained if the receiving elements are not in a symmetrical relationship.
From another aspect, an exemplary embodiment provides a method of obtaining positional information relating to an object, preferably in apparatus as aforesaid, the method comprising an operating cycle having m steps in which n=1, . . . m, each step comprising:                (a) generating a signal at a given timing relationship with respect to a transmitting trigger instant tn and transmitting it into a detection field; and        (b) receiving at a given timing relationship with respect to a receiving trigger instant rn at least a portion of the signal reflected from the object;        wherein the interval rn−tn varies as a function of n.        
Preferably the method further comprises: c) providing at least two (preferably spaced) receiving elements and identifying the values of n at which signals reflected from the object are received by the receiving elements. In this way, the time taken, and therefore the distance travelled, by the signals from the transmitting element to the various receiving elements can be determined.
In this method, step c) typically includes a step of cross-correlation of the signals received by two of the receiving elements. Preferably the cross-correlation function is a truncated cross-correlation function and comprises shifting one output signal with respect to another over a range which is less than the duration of the signals. Typically one output signal is shifted with respect to another over a range in which the maximum offset in either direction is less than the time that would be taken for the transmitted signal to travel directly from one receiving element to another.
In order to resolve a three-dimensional position of the object, step c) preferably includes a plurality or even multiplicity of steps of cross-correlation of the signals received by various of the receiving elements.
More information about the position and/or the nature of the object from which the signals were reflected may be obtained by including in step c) a comparison of the amplitude of signals received by various of the receiving elements. Moreover, step c) may include comparison of characteristic features of the received signals, such features including at least one of zero-crossings, maxima and minima.
In a preferred embodiment of this process, in which the correlation coefficient is approximately a cosinusoidal function of each offset angle (θ−θ0), where θ0 is the angle offset of the object in the plane containing the relevant antenna pair and the antenna boresight direction), it may not be necessary in step c) to carry out a finely-stepped cross-correlation, but to determine the correlation coefficients at a small sample of angles, separated by less than half the sinusoidal wavelength, to estimate the direction of the maximum, followed by further samples close to that direction to refine the estimate. This further shortens the truncated cross-correlation process.
After carrying out the truncated cross-correlation process, the method may include a step of selecting reflections denoted by correlation maxima which exceed a predetermined signal threshold (which may depend on the noise amplitude observed), and dividing each such correlation maximum by the gain of the transmitting and receiving antennas in the measured direction. Each such correlation maximum may then be multiplied by the fourth power of the measured range, to obtain a value proportional to the radar cross-section of the object. This value may then be compared to a cross-section threshold such that objects whose cross-section exceeds such threshold are reported or may be subjected to further processing.
In a further processing step each three-dimensional position determined in step c) may be compared with a description, either in the form of a look-up table or of an algorithm, which describes a volume of space near the antenna. The space may be selected such that the presence of an object within it is of relevance to a particular situation in which the method is being employed. This space will be referred to as “the warning zone”. Objects that are found to be within the warning zone and which exceed either a signal threshold or a cross-section threshold may then be reported, may give rise to a warning, or may be subjected to further processing.
In general, the range of values of rn−tn for 1≦n≦m may cover a range of time within which it is expected that a signal reflected from the object will be received. This can ensure that a reflection can be received from an object located anywhere within an intended detection field of the apparatus.
Further Aspects
In a preferred apparatus in accordance with an exemplary embodiment, an array of electromagnetic antennas is used in conjunction with processing electronics in a wideband microwave or millimeter imaging sensor suitable for obstacle detection, proximity and approach sensing or inspection. Objects in the volume in front of the array are resolved in range so that substantially only one is found at any one value of range. The range of any such object is determined b the time of flight of a pulsed signal reflected from it, and its angular position is then resolved, as taught in published International patent application No. WO97/14058, by determining the relative times at which such signals received from that object arrive at different elements of the array. In exemplary embodiments an array is configured with two or more elements separated by a distance which is less than or comparable with the dominant wavelength in the radiated pulse; the signals are pre-processed by frequency scaling rather than or in addition to frequency shifting, and both angular resolution and high detection performance are obtained by processing a combination of the channel outputs according to the element separation to determine timing offsets and angular positions. Wide bandwidth combined with precise inter-element receiver timing allows many targets within the range of the sensor to be resolved in range and uniquely positioned in angle.
A method in accordance with an exemplary embodiment may provide an image of an environment in conditions that human vision is compromised. For example, vision may be compromised by the physiological condition of a user (e.g. due to a physical disability). Alternatively or additionally which vision may be compromised by environmental conditions such as darkness, smoke or fog.
A method in accordance with an exemplary embodiment may also be applied to imaging within or through a solid object, such as a wall.
From yet another aspect, there is provided an electromagnetic imaging sensor comprising wideband signal transmitting means and a plurality of wideband receiving means, with associated antenna means in fixed relative positions within an assembly suitable for attachment to road vehicles or as portable equipment, timing signal generator means, control and processing means and connection means for connection to alarms, indicators or other systems, in which:                the transmitting means is operable to emit a train of electromagnetic pulses each less than or comparable with 1 nanosecond in duration, and characterised by a dominant wavelength or period, but containing substantially a small number of cycles of such wavelength or period,        the receiving means and timing signal generator means are operable to control the transmitting means to emit electromagnetic pulses and the receiving means to receive reflections of such pulses from objects in the field of view of the sensor and convert them to signals in which each frequency component is reduced by a constant factor, and the time domain waveform is stretched by the inverse of the same factor, and the arrival time of each component at the receiving elements is measured, being proportional to the distance to the object,        the pulses are of sufficiently short duration that reflections from such objects separated by a distance comparable with 0.1 meter or more in range are substantially resolved in time as they return to the receiving elements,        the arrival times of the reflections from each such object at each receiving element are subjected to a delay measurement process to determine the relative delays in arrival and therefrom derive the direction of the arrival from that object, thus determining its angular position in one, two or three dimensions with respect to the array of antennas.        
In an electromagnetic imaging sensor according to the last-preceding paragraph, the transmitting and/or the receiving means may be embodied in a single microchip, with the associated antenna feed elements printed on one or more adjacent printed circuit cards. The antennas themselves may be either part of the cards, or separate from them. The timing signal generator means and control and processing means are preferably embodied in the same single microchip. In such embodiments, the transmitting means may comprise a semiconductor switching device or amplifier external to the said microchip. Moreover, the receiving means may comprise one or more semiconductor switching devices, amplifiers, filters or pulse shaping networks external to the said microchip.
In one embodiment, both transmitting and receiving means comprise external semiconductor switching devices or amplifiers, and the timing signal generator and control and processing means are embodied in a single microchip. Alternatively, both transmitting and receiving means comprise semiconductor switching devices or amplifiers, and the timing signal generator and control and processing means are embodied in two separate microchips, or on a single chip.
In exemplary embodiments, the receiving means may comprise switching samplers in which the switch may be closed for an aperture time less than or comparable with one half the period of said dominant period.
Most preferably, the receiving means comprise switching samplers in which the switches are all closed by a common signal without intervening pulse generating circuits. In such embodiments, the switching samplers are advantageously electrically separated by lengths of transmission line whose electrical length exceeds or is comparable to one half the duration of said aperture time.
In a preferred construction, the antennas are patch antennas such as microstrip patches. This arrangement has advantages for manufacture. The antennas may be fed by a slotline feed in the circuit card carrying the transmitting means. Advantageously, the patches may be stacked patches. This arrangement assists in achieving the bandwidth necessary for the antennas.
The delay measurement process may include a cross-correlation process. Advantageously, the cross-correlation process is a truncated correlation process in which the range of the correlation determined between the signals received by any two elements is related to the spatial separation of those two elements. Additionally or alternatively, the delay measurement process comprises measurement of the timing difference between comparable features of the waveform such as zero-crossings, peaks, troughs, etc.
The control and processing means may also comprise classification means to identify classes of object near to the sensor by pattern matching with the reflected signals. Thus, the distance and angular position of each object from which signals are reflected may be used to identify the positions of a plurality of those objects in two or three dimensions. Thereafter, the positions of said plurality of said objects may be combined to form an image of the contents of the space near or in front of the sensor.
In embodiments of this aspect, the control and processing means may comprise or may be connected to further processing means in which successive such images or the signals from which they were generated are used in a synthetic aperture or inverse synthetic aperture process to further detail the image of the contents of the space near or in front of the sensor.
When two objects occur at substantially the same range from the apparatus, a single angular position may be derived corresponding substantially to the mean of the positions of the objects weighted by the amplitudes of said reflections of said pulses.
In a related aspect, an exemplary embodiment provides apparatus for obtaining positional information relating to one (or more) object(s), the apparatus comprising:                an array including a transmitting element and a receiving element (preferably a plurality of spaced receiving elements);        signal generating means for applying (operable to apply) a series of pulses to the transmitting element to cause it to transmit a signal, such that at least a portion of the signal can be reflected from the object to be received by the receiving element;        detection means for detecting (operable to detect) a signal reflected to the receiving element (during a detection aperture period) and for generating (operable to generate) an output signal representative of the received signal; and        timing means for operating the detection means at a varying delay.        
The timing means may be adapted or operable to initiate operation of the detection means after a variable interval following each operation of the signal generating means, the said interval varying with successive pulses.
If a plurality of receiving elements is provided, the computation means may be adapted or operable to process signals detected by the detection means, assess the time interval between a single reflected signal arriving at two or more of the receiving elements, and thereby determine the position of the object from which the signals were reflected.
In a further related aspect, an exemplary embodiment also provides apparatus for obtaining positional information relating to an object, the apparatus being operative in an operating cycle having m steps in which n=1, . . . m, the apparatus comprising:                a signal generating stage for generating a signal at a given timing relationship with respect to a transmitting trigger instant tn;        a transmitting element to transmit the said signal into a detection field; and        a receiving element for receiving at least a portion of the signal reflected from the object at a given timing relationship with respect to a receiving trigger instant rn;        wherein the interval rn−tn varies as a function of n.        
An exemplary embodiment may also extend to apparatus for obtaining positional information relating to one or more objects, the apparatus comprising:                an array including a transmitting element and a plurality of spaced receiving elements;        signal generating means operative to apply a series of pulses to the transmitting element to cause it to transmit a signal, such that a portion of the signal can be reflected from one or more objects to be received by the receiving elements;        detection means operative to detect signals reflected to the receiving elements during a detection aperture period and to generate an output signal representative of the received signals;        timing means operative to initiate operation of the detection means after a variable interval following each operation of the signal generating means, the said interval varying with successive pulses;        computation means operative to process signals detected by the detection means, assess the time interval between a single reflected signal arriving at two or more of the receiving elements, and thereby determine the position of the object from which the signals were reflected.        
An exemplary embodiment may further extend to apparatus for obtaining positional information relating to one or more objects, the apparatus being operative in an operating cycle for each of m steps in which n=1, 2 . . . m, the apparatus including:                a signal generating stage operative, simultaneously with or at a fixed time after a transmitting trigger instant tn to generate a signal, and a transmitting element to transmit the said signal into a detection field;        plurality of spaced receiving elements operative simultaneously with or at a fixed time after a receiving trigger instant rn to receive a portion of the signal reflected from one or more objects in the detection field, the interval rn−tn varying as a function of n and having a magnitude in a range corresponding to the times of travel of a signal reflected from an object within the detection field;        means for identifying the values of n at which signals reflected from one object received at two or more receiving elements and thereby assessing the time taken, and therefore the distance travelled, by the signals from the transmitting element to the various receiving elements; and        means for calculating the position of the object from the various path lengths thereby identified.        
An exemplary embodiment additionally provides apparatus for generating an image of objects within or through a solid object in accordance with any of the preceding aspects. In such cases, the solid object is a typically a wall.
An exemplary embodiment further provides apparatus in accordance with any of the preceding aspects of the exemplary embodiment for providing an image of an environment in conditions that human vision is compromised. For example, in such embodiments, vision may be compromised by the physiological condition of a user. Alternatively or additionally, vision might be compromised by environmental conditions.
In addition to all of the above, an exemplary embodiment provides apparatus for obtaining positional information relating to an object, comprising: transmitting means for transmitting a probe signal towards the object, the transmitting means comprising: a signal generating stage; and at least one transmitting element; receiving means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object, the receiving means comprising; at least one receiving element at the plurality of spaced apart locations; and detecting means for detecting the relative timing of the returned probe signals as received at the plurality of locations, the detecting means comprising; a detection stage, coupled to the receiving means; whereby positional information for the object can be determined from the relative timing; and wherein: the signal generating stage applies a series of m pulses to the transmitting element to cause it to transmit a signal, at times tn where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements; the detection stage detects a signal reflected to the receiving elements at times rn and generates an output signal representative of the received signal; and wherein the value of rn−tn varies as some function of n.
An exemplary embodiment provides apparatus for obtaining positional information relating to an object, comprising: means for transmitting a probe signal towards the object, said transmitting means comprising a transmitting element; means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object, said receiving means comprising a plurality of receiving elements; and detecting means, coupled to the receiving means, for detecting the relative timing of the returned probe signals as received at the plurality of spaced apart locations; whereby the positional information for the object can be determined from said relative timing; and wherein the transmitting element and receiving elements are disposed on a common substrate.
And it provides an antenna array optionally for use in apparatus for obtaining positional information relating to an object embodying one or more aspects, the array including a transmitting element and a plurality of receiving elements, the transmitting and receiving elements being disposed on a common substrate.
An exemplary embodiment further provides a method of obtaining positional information relating to an object, comprising the steps of: transmitting a probe signal towards the object; receiving, at a plurality of spaced apart locations, the probe signal as returned by the object; detecting the relative timing of the returned probe signals as received at the plurality of locations; and determining positional information for the object from the relative timing; wherein: the transmitting step comprises applying a series of m pulses to a transmitting element to cause it to transmit a signal, at times tn where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received at the plurality of spaced apart locations; the detecting step comprises detecting a signal reflected to the receiving elements at times rn and generating an output signal representative of the received signal; and wherein the value of rn−tn varies as some function of n.
An exemplary embodiment also provides a method of obtaining positional information relating to an object using an apparatus comprising a transmitting element, a receiving means comprising a plurality of receiving elements and a detecting means, the method comprising: transmitting a probe signal from the transmitting element towards the object; receiving, at a plurality of spaced apart locations, the probe signal as returned by the object; and detecting, at the detecting means, the relative timing of the returned probe signals as received at the plurality of spaced apart locations; determining the positional information for the object from said relative timing; wherein the detecting means is coupled to the receiving means and the transmitting element and receiving elements are disposed on a common substrate.
An exemplary embodiment further provides the use of an electromagnetic antenna array in a method described above in which the receiving elements are spaced apart by a distance that is the same order of magnitude as the wavelength λ of the radiation that it is intended to transmit and receive, the electromagnetic antenna array including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.
An exemplary embodiment also provides the use of an electromagnetic antenna array in a method of obtaining positional information relating to an object, the array including a transmitting element and at least three receiving elements arranged non-collinearly, the transmitting and receiving elements being disposed on a common substrate.
An exemplary embodiment further provides the use of an electromagnetic antenna array in a method of obtaining positional information relating to an object, the array including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.
An exemplary embodiment provides for a vehicle substantially as herein described and with reference to the accompanying drawings.
Additionally, an exemplary embodiment provides a control system for air bags in a motor road vehicle substantially as herein described and with reference to the accompanying drawings.
An exemplary embodiment also provides for apparatus for a land vehicle substantially as herein described and with reference to the accompanying drawings.
An exemplary embodiment provides for a device for obtaining information about objects within or through a wall substantially as herein described and with reference to the accompanying drawings.
An exemplary embodiment also provides for a hand-held tool substantially as herein described and with reference to the accompanying drawings.
There is also provided an electromagnetic microwave antenna array substantially as herein described and with reference to the accompanying drawings.
There is also provided apparatus for generating an image of objects within or through a solid object substantially as herein described and with reference to the accompanying drawings.
There is also provided apparatus, optionally for use on a (for example, land) vehicle, for obtaining positional information relating to an object substantially as herein described with reference to the accompanying drawings.
There is also provided a method for controlling deployment of air bags in a vehicle substantially as herein described.
Features of any aspect of an exemplary embodiment may be combined with or interchanged with features of any other aspect as desired. Method features may be applied to apparatus aspects and vice versa. Features which are provided independently may be provided dependently, and vice versa.
Although the embodiments of an exemplary embodiment that will be described below operate by radiating ultra-high-frequency, microwave or millimeter wave radiation, in principle a range of other types of signals could be used in alternative embodiments. For example, embodiments could be constructed which operate in other parts of the RF spectrum, they could use light, or they could use sound waves such as ultrasound.